I’m pretty sure the main use is observing dangerous environments like mines, places with toxic waste, and oil rigs. The payload will usually be used for sensors or a door opening device, not to transport cargo.
This could be a good use. Mines in particular where drones would be impractical. I'm not so sure about oil rigs, while Spot would be great on the stairs/ terrain, it has trouble with seeing the edge of cliffs and might well march right off into the ocean.
Probably the biggest advantage would be the ability to take samples or hold some kind of special equipment.